This invention relates generally to devices useful in measuring and monitoring functional parameters of the human body. More particularly, the invention relates to sensors useful in the monitoring of respiration The sensors of the invention may be used in monitoring respiration under stress-free situations, such as during sleep, and may also be used under conditions of stress, such as during a lie detector test.
Various transducers useful in measuring respiration of the human organism may be found in the prior art. The following U.S. Patents, each of which are herein expressly incorporated by reference, are exemplary thereof.
U.S. Pat. No. 3,782,368 describes a transducer assembly comprising a piezoelectric element, an elastic belt, a fastening means, and specialized signal conditioning circuitry of various functions.
U.S. Pat. No. 4,185,621 describes a body worn parameter display devices which includes a housing having a display array, a piezoelectric sensing means for sensing a variable body pressure and delivering a representative electrical signal, a means for connecting the electrical output to the display array, and a means for supplying the piezoelectric means with electricity. The device is worn like a wristwatch and thus the piezoelectric elements are thus attached to the patient using a belt means.
U.S. Pat. No. 4,443,730 describes a multi-layer transducer device for attachment to the body. The device is attached by means of a cuff, which is the functional equivalent of a belt.
U.S. Pat. No. 4,576,179 describes a respiration monitoring device having a piezoelectric transducer mounted in a bridge-like arrangement on a pair of spaced piers that are connected by a flexible beam member. The sensing element of the device is attached to the patient by means of a belt.
U.S. Pat. No. 4,909,260 sets forth a belt adapted to fit on a body so as to undergo tension changes due to body expansion and contraction during breathing wherein the belt has a first sensing means with a preferential sensing axis for producing a breathing signal in response to opposing forces along the sensing axis and a holder means interposed in the belt as part thereof that operatively holds the sensing means with its sensing axis aligned generally transverse to tension in the belt, and for transforming a tension change in the belt at the sensing means to opposing forces directed along the transverse sensing axis to produce a breathing signal.
U.S. Pat. No. 4,960,118 sets forth a method for measuring respiration which includes measuring the rate of change of abdomen circumference using a piezoelectric sensor that provides an electrical output, with the piezoelectric sensor being attached to an extensible abdominal belt by means of a rivet, in which the piezoelectric sensor has an electrically-conductive coating on each of its sides. The rate of change of rib cage circumference is also measured using another piezoelectric sensor, with the piezoelectric sensor being attached to an extensible abdominal belt by means of a rivet, in which the piezoelectric sensor has an electrically-conductive coating on each of its sides. The outputs of the rib cage and abdominal sensors are weighted and summed so that the summed output represents total respiratory flow.
U.S. Pat. No. 5,002,060 sets forth a monitoring system adapted to simultaneously monitor cardiac and respiratory rates and characteristics and substantial changes in temperature of a living body. The system uses sensors which are passive and non-invasive, and remotely completely located off the living body such as piezoelectric sensors. The sensor means is adapted to detect respiration and heart beat signals, and is passive and remotely located off the body of the individual.
U.S. Pat. No. 5,161,541 sets forth an apparatus for monitoring respiration of a patient that includes a flexible substrate having three thermoresistive devices comprising a layer of conductive ink of high temperature coefficient of resistivity coupled in series and affixed to a substrate. There is a means for adhesively attaching the substrate to the patient using a strip of medical adhesive tape. No mention is made of a piezoelectric sensor, and no filtering circuitry is present on the sensing means.
U.S. Pat. No. 6,021,351 sets forth 1. Apparatus for assessing the well-being of a patient in whom a cardiac pacemaker is implanted to assess the efficacy of a given pacing therapy, comprising a sensor means for detecting a physiologic parameter of a patient on or in whom the sensor means is affixed and for producing electrical signals that vary with the patient""s level of exertion. The sensor means may be a piezoelectric sensor. There is no specific mention of the means by which the sensor is attached to the patient, nor of the presence of any filtering circuitry in the transducer itself.
U.S. Pat. No. 6,024,088 teaches a breath-synchronization control unit for a gas feeder for supplying a gas from a source to a human in synchronization with breathing. The unit includes a breath-detecting sensor, wherein the breath detecting sensor includes a plate shaped piezoelectric element, a container having a single space to house said piezoelectric element, and a control section which opens and closes a valve of a gas source to supply gas for a predetermined time when said piezoelectric element of the breath-detecting sensor detects an inhalation attempt by sensing air pressure from the air vent hole.
U.S. Pat. No. 6,064,910 discloses a respiration detector that includes a sensor which generates an electrical signal containing a signal component produced by heart sounds, wherein the signal component has a varying amplitude. There is also an analyzer means for extracting the signal component and for analyzing variations of the amplitude of the signal component for identifying at least one of a respiration rate, and a respiration depth from the variations of the amplitude. No adhesive tape is disclosed and no filtering circuitry is disclosed as being a part of the transducing means.
Reissue U.S. Pat. No. 32,180 sets forth a flexible composite sheet which comprises layers which function as electromechanical transducers for a patient who lies upon them. No filtering circuitry is disclosed as being part of the construction and no mention is made of adhering the transducer to the body of a patient.
However, the teachings of the prior art suffers from the use of straps or belts to cause the prior art sensors to contact the subject person""s body. The use of straps is undesirable because over even relatively short periods of time, normal movements of a patient""s body cause the sensors which are held in place by such straps to become loosed from the straps and hence unable to collect the desired data. This situation is especially troublesome for those engaged in the study of sleep disorders, as such sensors routinely slide to incorrect body positions or fall off the patient during the evening.
Further, of the sensing means found in the prior art, none has thus far provided filtering circuitry which is part of an integral construction with the sensor itself Rather, the prior art has relied exclusively on remotely located filtering circuitry. Such separation of the location of the filtering circuitry and the sensor has lead to an increased electronic noise level, owing to the length of the wire between these elements.
Thus, if a respiratory sensor having a filtering circuit as an integral part of its construct were devised, such a device would provide a data acquisition device with more accuracy than its prior art counterpart. In addition, if such a sensor were also attachable to a human subject in such fashion as to be relatively un-noticeable, then the human subject would sense less anxiety associated with the wearing of such a sensor. Finally, if such means for attaching a sensor by such relatively un-noticeable fashion enabled the sensor to remain on a patient during their entire course of sleep during a study requiring monitoring of the person in the sleep state, such a device would enable uninterrupted data gathering and less re-testing than is associated with analogous sensors in the prior art. It is believed that if such a device displayed all of these characteristics there would be provided added benefit as well, owing to the combined effects of uninterrupted gathering of data, more comfortable mounting, and a decreased noise level, which are believed to complement one another to provide a synergy not available prior to the discovery of the present invention. The present invention provides such devices.
The present invention provides a substantially planar device useful for measuring respiration of a human subject and which may be directly attached to a human subject. A device according to the invention comprises in a single construction both a transducer that is capable of generating a voltage signal output in response to the motion of the torso during human respiration, and a filtering circuit connected to the output of the transducer, so as to reduce electrical noise levels. Such an arrangement enables a device according to the invention to be affixed to a patient not only by belts used conventionally for this purpose, but importantly enables such single construction to be affixed to a human subject by means of adhesive tape. Such a capability provides for the secure fitment of the device as a whole to the subject, in such fashion as to minimize discomfort and to ensure that the transducer does not become dislodged from its initial placement.
The invention also provides novel means using a plurality of adhesive tapes by which such a device is affixed to a subject, although a single piece of adhesive tape may be used, if desired.